Orbitronics: Orbital Currents in Solids

Abstract

In solids, electronic Bloch states are formed by atomic orbitals. While it is natural to expect that orbital composition and information about Bloch states can be manipulated and transported, in analogy to the spin degree of freedom extensively studied in past decades, it has been assumed that orbital quenching by the crystal field prevents significant dynamics of orbital degrees of freedom. However, recent studies reveal that an orbital current, given by the flow of electrons with a finite orbital angular momentum, can be electrically generated and transported in wide classes of materials despite the effect of orbital quenching in the ground state. Orbital currents also play a fundamental role in the mechanisms of other transport phenomena such as spin Hall effect and valley Hall effect. Most importantly, it has been proposed that orbital currents can be used to induce magnetization dynamics, which is one of the most pivotal and explored aspects of magnetism. Here, we give an overview of recent progress and the current status of research on orbital currents. We review proposed physical mechanisms for generating orbital currents and discuss candidate materials where orbital currents are manifest. We review recent experiments on orbital current generation and transport and discuss various experimental methods to quantify this elusive object at the heart of $orbitronics$ $-$ an area which exploits the orbital degree of freedom as an information carrier in solid-state devices.

Invited article from EPL Perspective

References in corpus (14)

• Study of Intrinsic Spin Hall Effect and Orbital Hall Effect in 4d- and 5d- Transition Metals
• Orbital magnetization in periodic insulators
• Giant Orbital Hall Effect in Transition Metals: Origin of Large Spin and Anomalous Hall Effects
• Robustness of the Spin-Chern number
• Quantum Theory of Orbital Magnetization and its Generalization to Interacting Systems
• Maximal Rashba-like spin splitting via kinetic energy-driven inversion symmetry breaking
• Theory of orbital magnetoelectric response
• Orbital Rashba effect in surface oxidized Cu film
• Intrinsic orbital and spin Hall effects in monolayer transition metal dichalcogenides
• Prototypical topological orbital ferromagnet $\gamma$-FeMn
• Orbital Magnetic Moment of Magnons
• Orbital momentum Hall effect in p-doped graphane
• Phonon rotoelectric effect
• Current-induced torque originating from orbital current